1. Field of the Invention
The invention relates to a measuring device with a DC voltage amplifier especially for measuring the envelope power and/or the mean power of a high-frequency signal.
2. Discussion of the Background
A measuring device is known from DE 199 55 342 A1. The envelope power and also the mean-power or RMS values can both be measured with the measuring device disclosed in this document. In order to cover the largest possible dynamic range, the measuring device is subdivided into several individual ranges, which are each allocated to several measuring branches disposed in parallel. A chopper is arranged in each measuring branch. All choppers are controlled synchronously. Moreover, an analog/digital converter, which is supplied with a synchronous clock-pulse rate, is disposed in each measuring branch. After a weighted addition of the digitized measuring signals of the individual measuring branches, a synchronous demodulation is implemented before the signal is evaluated.
The use of parallel measuring branches in the measuring device known from DE 199 55 342 A1, which is associated with an extremely complex design for the measuring device, is disadvantageous. In addition to the synchronization of the choppers and the analog/digital converters, it must be ensured that the group delay time of the measured signal is of exactly the same value in all measuring branches. Especially in the video bandwidths to be realized in the order of magnitude of 30 MHz, this causes difficulties in practice. With a single-path realization of the measuring device, an adequate compression of the dynamic range must be ensured. Moreover, an amplifier with low noise influence and low temperature dependence of the transmission characteristic is required.